1. Field of the Invention
Silicon carbide's unique combination of properties make it a particularly suitable material for a variety of applications in the semiconductor, optical, electronic and chemical processing fields. Some potential applications, however, have been limited by the intrinsic high electrical resistivity of silicon carbide. This invention is directed to chemical vapor deposited low resistivity silicon carbide (CVD-LRSiC) having an electrical resistivity of less than 0.9 ohm-cm., and, especially, to free standing articles made of such CVD-LRSiC. Such articles are particularly useful in high temperature furnaces, such as semiconductor processing furnaces and plasma etching apparatus.
2. Background of the Invention
Silicon carbide, particularly silicon carbide produced by chemical vapor deposition (CVD-SiC), has unique properties which make it a material of choice in many high temperature applications, several of which are reviewed in U.S. Pat. No. 5,683,028. Pure CVD-SiC has relatively high electrical resistivity. While this is a desirable characteristic for certain applications, it is a limitation restricting its use in other applications. Certain components, such as the plasma screen, focus ring and edge ring used in plasma etching chambers need to be electrically conductive as well as possess high temperature stability. While the high temperature properties of CVD-SiC have made it a material of choice for use in such chambers, its high resistivity has limited its use in fabricating those components which require a greater degree of electrical conductivity.
The high electrical resistivity of CVD-SiC has further restricted its use in applications which are subject to the build-up of static electricity. The need to ground components used in such applications requires that they possess greater electrical conductivity than is generally found in CVD-SiC. A low resistivity silicon carbide would provide a unique and useful combination of high temperature properties with suitable electrical conductivity properties for use in applications where grounding is required.
Moreover, the combination of relatively low electrical resistivity with the high temperature properties of CVD-SiC, suggest the suitability of such CVD-SiC for fabrication into a variety of high temperature electrical components such as electrodes, heating elements, etc.
The chemical vapor deposition process for producing free standing silicon carbide articles involves reacting vaporized or gaseous chemical precursor in the vicinity of a substrate to result in silicon carbide depositing on the substrate. The deposition reaction is continued until the deposit reaches the desired thickness. The deposit is then separated from the substrate as a free-standing article which may or may not be further processed by shaping, machining, polishing, etc. to provide a final silicon carbide article.
In a typical chemical vapor deposition silicon carbide production run, a silicon carbide precursor gas, such as a mixture of methyltrichlorosilane (MTS), hydrogen and argon, is fed to a deposition chamber where it is heated to a temperature at which it reacts producing silicon carbide. The silicon carbide deposits as a layer, or shell, on a solid mandrel provided in the deposition chamber. After the desired thickness of silicon carbide is deposited on the mandrel, the coated mandrel is removed from the deposition chamber and the deposit separated therefrom. Monolithic silicon carbide plates and cylinders have been produced by applying such chemical vapor deposition (CVD) techniques with suitably shaped substrate or mandrel forms. Several CVD-SiC deposition systems are described and illustrated in U.S. Pat. Nos. 5,071,596; 5,354,580; and 5,374,412, which are incorporated herein by reference.